1. Field of the Invention
The invention relates to an apparatus for treating exhaust gases from a mobile internal combustion engine, having at least an exhaust pipe with a direction of extent, a honeycomb body including at least ceramic or extruded material, and at least one metallic fiber mat, which is at least partially disposed between the exhaust pipe and the honeycomb body. The preferred application area for the invention is vehicles, in particular automobiles.
The exhaust systems of mobile internal combustion engines are exposed to considerable thermal and dynamic stresses. They result on one hand from the combustion processes themselves and on the other hand also from the movement of the vehicle. The fluctuating load conditions in the internal combustion engine lead to differing exhaust gas temperatures, exhaust gas compositions, pressure surges, etc. The result thereof is that the components of the exhaust system are also subject to fluctuating thermal stresses. In particular, if the components of the exhaust system include different materials, the respective thermal expansion properties are constantly imposing new demands on the connection between those components and with a view to ensuring that the components remain at the intended position in the exhaust system in the long term. In that context, particular attention needs to be paid to the securing of a honeycomb body, which is produced from ceramic or extruded material, with respect to a usually metallic exhaust pipe.
With configurations of that type, it is known that different thermal expansion properties of the honeycomb body and the exhaust pipe can be compensated for by compensation layers which are disposed between the honeycomb body and the exhaust pipe. That usually involves the use of what are known as swellable mats, which have an ability to take up water. By taking up water contained in the exhaust gas, the mats swell and thereby prevent the assembly formed from the honeycomb body, the swellable mat and the exhaust pipe from coming loose. However, a problem with those swellable mats is that they do not generally satisfy the dynamic requirements in the long term, so that the swellable mat can become partially detached. There is also a risk of the constituents which are dissolved out of the swellable mat being volatilized, and the effect thereof on the environment has not yet been fully clarified.
Another known way of compensating for the different thermal expansion properties is to use spring elements, for example in the form of sleeves, spacers, etc., which are likewise positioned between the honeycomb body and the exhaust pipe. They may also form spaces which are provided with damping materials, such as for example high-temperature-resistant, free-flowing granules or powders. However, constructions of that type are somewhat complex to produce and in some cases are likewise unable to guarantee a long service life.
Moreover, it is also known that knitted metallic wire fabrics can be laid between a ceramic honeycomb body and a metallic exhaust pipe. Examples of such configurations include U.S. Pat. No. 4,158,037 and German Published, Non-Prosecuted Patent Application DE 38 04 559 A1.